A number of conventional pressure sensors are able to be used to record a combustion chamber pressure of an internal combustion engine, both in Otto engines and in Diesel engines. Such devices make up a predominant component of modern engine controls, since the combustion chamber pressure has to be recorded very accurately, particularly for the purpose of reducing fuel consumption and emissions.
For instance, German Patent Application No. DE 10 2009 026 436.1 describes various devices for recording a combustion chamber pressure of an internal combustion engine. In this combustion chamber pressure sensor, a sensor housing, on the combustion chamber side, has at least one opening that is closed by at least one diaphragm. Within the sensor housing, at least one mechanical-electrical transducer element is accommodated, at least one transmitting element, that is developed separately from the sensor housing, being provided for transmitting a deformation of the diaphragm to the mechanical-electrical transducer element.
Thus, for the sealing of the sensor housing in combustion chamber pressure sensors from the combustion chamber surroundings, usually, flexible diaphragms, such as metal diaphragms, are used, as shown, for instance, in German Patent Application No. DE 10 2009 026 436.1. Because of their rigidity, which is slight, to be sure, but nevertheless exists, these diaphragms are usually a part of a so-called force path or force transmission path, via which one, or via which several, if several are present, of the forces created by the combustion chamber pressure are transmitted to the actual sensor element, for instance, the mechanical-electrical transducer element. Now, during a combustion process, if a flame front at least partially reaches a diaphragm surface, in the diaphragm there comes about an overtemperature having a gradient between the front side facing the combustion chamber and the rear side situated on the opposite side. Consequently, a temperature profile sets in synchronously with the flame front. However, this temperature profile causes a deformation of the diaphragm, generally, which, as a reaction force, has an effect on the force path, and is thus superposed on the desired pressure signal as an error signal. This error signal occurring with the time constant of a combustion cycle is also designated as thermoshock or short-time drift. Indirect measures may be taken to avoid or reduce this effect. For example, a flame front may be shielded. However, such indirect measures generally involve the danger of a reaction of these measures on a pressure curve at the diaphragm, which may also lead to signal errors.
Therefore, a combustion chamber pressure sensor would be desirable which would, at least to a great extent, avoid the abovementioned effects. In particular, the avoidance of these effects should be based on direct measures which have as small an effect as possible on the actual pressure curve to be measured, and which preferably, at least to a great extent, reduce the thermoshock effect described by a geometrical design of the diaphragm.